Adjustable-angle spinal fixation element

ABSTRACT

A spinal fixation device is provided having first and second elongate members that are angularly adjustable relative to one another. Each elongate member can include a connecting feature formed on a terminal end thereof, and each connecting feature can be coupled to one another to allow angular movement of the first and second elongate members. The device can also include a locking mechanism that is adapted to couple to the connecting feature on each of the first and second elongate members to lock the elongate members in a fixed position relative to one another.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 11/873,847 filed on Oct. 17, 2007 and entitled “Adjustable-Angle Spinal Fixation Element,” which is a divisional of U.S. patent application Ser. No. 10/708,919 filed on Mar. 31, 2004 and entitled “Adjustable-Angle Spinal Fixation Element,” which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present application relates to devices for use in spinal surgery, and in particular to spinal fixation devices having an adjustable angle.

BACKGROUND OF THE INVENTION

Stabilization of the spine is often required following trauma, tumor, or degenerative pathologies. Although each region of the spine presents unique clinical challenges, posterior fixation of the cervical spine is particularly challenging. The anatomy of the cervical spine makes it a technically challenging area to instrument. Specifically, several vital neural and vascular structures, including the vertebral arteries, nerve roots, and spinal cord, must be avoided during surgery.

Current methods of posterior cervical stabilization include the use of an occipital spinal plate and a transition rod for fixation of the cervico-thoracic junction. Such devices typically include a spinal fixation element, such as a relatively rigid fixation rod, that is coupled to adjacent vertebrae by attaching the element to various anchoring devices, such as hooks, bolts, wires, or screws. Often two rods are disposed on opposite sides of the spinous process in a substantially parallel relationship. The fixation rods can have a predetermined contour that has been designed according to the properties of the target implantation site, and once installed, the rods hold the vertebrae in a desired spatial relationship, either until healing or spinal fusion has taken place, or for some longer period of time.

It is often the case that the predetermined contour of a fixation rod does not exactly fit the contour of the implantation site. This may be attributed to various factors including a patients age, which directly relates to the size of their spinous process, irregular contouring due to disease or injury, or malformation due to a birth defect. These conditions often make it impossible to use a pre-contoured fixation rod. In these cases, multiple rods projecting at multiple angles are used, however such devices can complicate the surgery, as well as the recovery, and they can add undue strain on the spinous process, possibly resulting in an unsuccessful repair of the spine.

Accordingly, there presently exists a need for improved spinal fixation devices that can be easily installed and that allow for angular adjustment and subsequent locking. There is also a need for spinal fixation devices that have a low-profile to avoid potential irritation and injury to the patient.

SUMMARY OF THE INVENTION

The present invention generally provides a spinal fixation device having first and second elongate members that are angularly adjustable relative to one another. Each elongate member can include a connecting feature formed on a terminal end thereof, and each connecting feature can be coupled to one another to allow angular movement of the first and second elongate members. The device can also include a locking mechanism that is adapted to couple to the connecting feature on each of the first and second elongate members to lock the elongate members in a fixed position relative to one another.

In one embodiment, the connecting feature on the first elongate member is a female connector, and the connecting feature on the second elongate member is a male connector that is adapted to receive the female connector. The female connector preferably includes opposed arms defining a recess therebetween for receiving the male connector. A bore can extend through the opposed arms on the female connector and through the male connector for receiving a central mating element that is adapted to mate the male and female connectors to one another. In an exemplary embodiment, the central mating element is a cylindrical member that is adapted to allow at least one of the first and second elongate members to rotate thereabout. More preferably, however, the cylindrical member is fixedly coupled to a portion of the female connector, and the male connector is free to rotate about the cylindrical member.

In use, the locking mechanism can engage the cylindrical member to prevent movement of the male connector relative to the female connector. While a variety of locking mechanisms can be used, in one embodiment the locking mechanism can be in the form of a slot extending through the male connector such that the male connector is in the form of a clamp, and the locking mechanism can also include a fastening element that is adapted to engage the male connector to clamp the cylindrical member within the bore. The fastening element is preferably a threaded member.

In other aspects of the present invention, the connecting feature on each of the first and second elongate members can rotate about a central axis extending substantially perpendicular to an axis of each first and second elongate members. More preferably, each connecting feature can include opposed inner and outer surfaces, and the inner surface on each connecting feature can be in contact one another. In an exemplary embodiment, the inner surface on each connecting feature is adapted to prevent rotation of the first and second elongate members relative to one another when the locking mechanism is in a locked configuration. The connecting features can also optionally include anti-rotation features, such as gear teeth, formed on the inner surface of each connecting feature.

In further aspects, a first bore can extend through the inner and outer surface of the connecting feature on the first elongate member and a second bore extending through the inner and outer surface of the connecting feature on the second elongate member. In one embodiment, the bores can be adapted to receiving the locking mechanism, which can be, for example, a fastening element having a head and a shaft with threads formed thereon. The first bore is preferably non-threaded for freely rotatably receiving a portion of the shaft of the fastening element, and the second bore is preferably threaded for mating with the threads formed on the shaft of the locking mechanism.

In an alternative embodiment, a pin member can be disposed through the first and second bores extending through the inner and outer surfaces of the connecting feature, and the pin member can include a transverse bore extending therethrough for receiving at least a portion of the locking mechanism. A receiving bore can be formed in at least one connecting feature, and the receiving bore can be in communication with the central bore to allow the locking mechanism to extend therethrough and into the transverse bore in the pin member. In a further embodiment, the locking mechanism can be adapted to engage the pin member to translate the first and second connecting features toward one another to lock the first and second elongate members in a fixed position relative to one another.

In yet another embodiment of the present invention, the connecting feature on each of the first and second elongate members can be slidably coupled to one another. More preferably, the connecting feature on each of the first and second elongate members is a substantially curved terminal portion, and the terminal portion are complementary for slidably mating to one another. Each terminal portion can include a slot formed therein for receiving the locking mechanism. Each terminal portion can also include one or more anti-sliding surface features formed on a portion thereof to prevent movement of the first and second elongate members relative to one another when the locking mechanism is in a locked configuration.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1A is an exploded view of one embodiment of an adjustable-angle spinal fixation device having male and female connecting features according to the present invention;

FIG. 1B is a side, assembled view of the adjustable-angle spinal fixation device shown in FIG. 1A in a locked position;

FIG. 1C is a perspective view of a central mating element of the adjustable-angle spinal fixation device shown in FIG. 1A;

FIG. 1D is an enlarged perspective view of a male connector of the adjustable-angle spinal fixation device shown in FIG. 1A;

FIG. 1E is an exploded view of another embodiment of an adjustable-angle spinal fixation device having a spinal fixation plate with a male connecting feature and a spinal rod with a female connecting feature for mating to the male connecting feature;

FIG. 2A is an exploded view of another embodiment of an adjustable-angle spinal fixation device according to the present invention having anti-rotation features formed thereon;

FIG. 2B is an enlarged side view of the adjustable-angle spinal fixation device shown in FIG. 2A in a locked position;

FIG. 3A is an exploded view of an adjustable-angle spinal fixation device having a pin member for receiving a fastening element according to yet another embodiment the present invention;

FIG. 3B is a perspective view of the adjustable-angle spinal fixation device shown in FIG. 3A in a locked position;

FIG. 4A is a perspective view of yet another embodiment of an adjustable-angle spinal fixation device according to the present invention having substantially curved complimentary matable connecting features;

FIG. 4B is a side view of the adjustable-angle spinal fixation device shown in FIG. 4A in a locked position;

FIG. 5A is a side view of another embodiment of an adjustable-angle spinal fixation device according to the present invention having a locking mechanism that provides a polyaxial connection with first and second spinal fixation elements coupled thereto;

FIG. 5B is a top perspective view of the adjustable-angle spinal fixation device shown in FIG. 5B in a locked position; and

FIG. 5C is a bottom perspective view of the adjustable-angle spinal fixation element shown in FIG. 5A in a locked position.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides various angularly-adjustable spinal fixation devices, each of which generally includes first and second elongate members 12 a, 12 b, a connecting feature 20 formed on a terminal end of each of the first and second elongate members 12 a, 12 b, and a locking mechanism 30 that is adapted to lock the first and second elongate members 12 a, 12 b in a fixed position relative to one another. The elongate members 12 a, 12 b are preferably spinal rods and/or plates that are used, for example, in the stabilization of the spine following trauma, tumor, or degenerative pathologies. Among many other advantages, the devices are particularly useful to allow a spinal rod to be positioned and locked in a desired angular orientation without the need to reshape the rod, and without requiring the point of adjustment to be attached to the spine of a patient.

FIGS. 1A-1B illustrate one exemplary embodiment of a spinal fixation device 10 having first and second elongate members 12 a, 12 b, a connecting feature 20 a, 20 b formed on a terminal end 14, 16 of each of the first and second elongate members 12 a, 12 b, and a locking mechanism 30 that is adapted to lock the first and second elongate members 12 a, 12 b in a fixed position relative to one another. In use, the first and second elongate members 12 a, 12 b can be angularly adjusted relative to one another and, once properly positioned, they can be locked in a fixed position relative to one another using the locking mechanism 30.

The first and second elongate members 12 a, 12 b can each have any shape or size, and each elongate member 12 a, 12 b can vary in diameter relative to one another. The elongate members 12 a, 12 b can also vary in length depending on the intended use. In the illustrated embodiment, the first and second elongate members 12 a, 12 b are substantially cylindrical spinal rods, each having a terminal end 13, 15 that is adapted to mate to a spinal anchor, such as a hook, screw, bolt, plate, etc. The opposed terminal end 14, 16 of each elongate member 12 a, 12 b includes the connecting feature 20 a, 20 b formed thereon and mated to one another.

While the terminal ends 13, 15 of the elongate members 12 a, 12 b shown in FIGS. 1A-1B extend along the axis of the elongate members 12 a, 12 b, the terminal ends 13, 15 can extend at an angle relative to the elongate members 12, 12 b. For example, as shown in FIG. 1E, the terminal end 13′ of one of the elongate members, e.g., the first elongate member 12 a′, can extend at a 90° angle relative to the longitudinal axis of the second elongate member 12 b, as shown in FIG. 1E. In other embodiments, one or both of the elongate members can be in the form of a spinal fixation plate. For example, as shown in FIG. 1E, the second elongate member 12 b is in the form of a spinal fixation plate 12 b′, rather than a spinal rod.

Continuing to refer to FIGS. 1A-1B, each connecting feature 20 a, 20 b can have a variety of configurations, but they should be adapted to allow for angular adjustability of the first and second elongate members 12 a, 12 b relative to one another. In the embodiment shown in FIGS. 1A-1B, the connecting feature 20 a on the first elongate member 12 a is in the form of a female connector, and the connecting feature 20 b on the second elongate member 12 is in the form of a male connector. The terminal ends 14, 16 of the elongate members 12 a, 12 b can mate to the connectors 20 a, 20 b at any location, but in an exemplary embodiment the elongate members 12 a, 12 b are positioned such that the connectors 20 a, 20 b do not interfere with the patient's spinal anatomy.

While the male and female connectors 20 a, 20 b can have a variety of configurations, in an exemplary embodiment the female connector 20 a has opposed arms 23 a, 23 b that are spaced a distance apart from one another to form an open recess 26 therebetween for seating the male connector 20 b. Each arm 23 a, 23 b can vary in shape and size, but in an exemplary embodiment, as shown, the arms 23 a, 23 b each have a substantially circular shape. The male connector 20 b can also vary in shape and size, but it preferably has a shape that corresponds to the female connector 22, and more preferably the male connector 20 b is substantially circular.

Each connector member 20 a, 20 b also preferably includes a central bore 28 a, 28 b that extends therethrough in a direction that is substantially perpendicular to a longitudinal axis L₁, L₂ each of the first and second elongate members 12 a, 12 b. The central bore 28 a, 28 b is adapted to receive a central mating element 29 therethrough for mating the connectors 20 a, 20 b, and for allowing one or both connectors 20 a, 20 b to rotate thereabout. The central mating element 29 can have a variety of configurations, however FIG. 1C illustrates a central mating element 29 having a substantially cylindrical shape and including proximal and distal ends 29 c, 29 d. In a preferred embodiment, one of the connectors, e.g., the female connector 20 a, is configured to receive the mating element 29 such that the female connector 20 a and the mating element 29 are in a fixed position relative to one another, and the male connector 20 b is free to rotate about the mating element 29 and relative to the female connector 20 a. This can be achieved, for example, by providing complementary features on the mating element 29 and the female connector 20 a to prevent rotation relative to one another. As shown in FIGS. 1A-1C, the portion of the bore 28 a that extends through the first arm 23 a has a substantially square shape, and the distal end 29 d of the central mating element 29 includes a substantially square-shaped protrusion 29 a formed thereon and adapted to be disposed within the corresponding bore 28 a formed in the female connector 20 a. As a result, when the device 10 is in use, the female connector 20 a is locked in a fixed position relative to the mating element 29, but the male connector 20 b is free to rotate thereabout. A person skilled in the art will appreciate that the complementary features on the mating element 29 and the female connector 20 a can have a variety of other configurations and by way of non-limiting example, the complementary mating features can have a hexagonal shape, an octagonal shape, a D-shape, or any other shape that prevents rotation of the female connector 20 a relative to the mating element 29. In other embodiments, the mating element 29 and the female connector 20 a can be fixedly mated to one another, for example, by welding the components together, to prevent rotation of the female connector 20 a relative to the mating element 29.

As previously stated, the device 10 also includes a locking mechanism 30 that is adapted to lock the first and second elongate members 12 a, 12 b in a fixed position relative to one another. While virtually any technique can be used to lock the elongate members 12 a, 12 b in a fixed position, FIGS. 1A, 1B, and 1D illustrate an exemplary embodiment of a locking mechanism 30. In this embodiment, the male connector 20 b is in the form of a clamp mechanism and more particularly it includes a slot 25 extending therethrough and in communication with the central bore 28 formed therein, as shown in more detail in FIG. 1D. The slot 25 separates the male connector 20 b into upper and lower portions 24 a, 24 b that are movable between an open position and a closed position in which the male connector 20 b is adapted to engage the mating element 29 extending through the central bore 28 b.

In order to move the upper and lower portions 24 a, 24 b to the closed position, the male connector 24 can include a receiving bore 28 c formed therein and extending through the upper and lower portions 24 a, 24 b. The receiving bore 28 c is adapted to receive a fastening element 27 that is effective to pull one or both of the upper and lower portions 24 a, 24 b toward one another to close the slot 25. As a result, the central bore 28 b extending through the male connector 20 b is decreased in size, thereby allowing the male connector 20 b to engage the mating element 29 and preventing rotation of the second elongate member 12 b relative to the first elongate member 12 a.

The fastening element 27 that is disposed through the receiving bore 28 c can have a variety of configurations, and it can be, for example, a screw, anchor, or bolt. In the illustrated embodiment, as shown in FIG. 1A, the fastening element 27 is a threaded member, e.g., a screw, having a head 27 a and a thread shank 27 b. The receiving bore 28 c formed in the male connector 20 b can thus includes threads formed therein for mating with the threaded shank 27 b on the fastening element 27. More preferably, however, the portion of the receiving bore 28 c formed in the upper portion 24 a of the male connector 20 b is non-threaded to allow free rotation of the threaded member 27 with respect thereto, and the portion of the receiving bore 28 c formed in the lower portion 24 b of the male connector 20 b is threaded to mate with the threaded shank 27 b. This allows the fastening element 27 to pull the upper portion 24 a toward the lower portion 24 b, thereby locking the portions 24 a, 24 b relative to one another and locking the male connector 20 b relative to the mating element 29.

Those skilled in the art will appreciate that the receiving bore 28 b and male connector 20 b can be a variety of other configurations to facilitate locking of the male connector 20 b. By way of non-limiting example, the central mating element 29 and/or an inner surface of the bore 28 b on the male connector 20 b can have anti-rotation features formed thereon, such that when the male connector 20 b is closed the anti-rotation features can assist in securing the male connector 20 b around the central mating element 29. The anti-rotation features can be, for example, a non-slip coating applied to the surface of the mating element 29 and/or the bore 28 b, teeth or knurling formed on the surface of the mating element 29 and/or the bore 28 b, or other gripping features known to one skilled in the art.

In use, the fastening element 27 can be partially threaded into the bore 28 c formed in the male connector 20 b to allow the first and second elongate members 12 a, 12 b to rotate relative to one another. Although the elongate members 12 a, 12 b can be adapted for multi-axial rotation, in the illustrated embodiment the elongate members 12 a, 12 b rotate along a single plane. Each elongate member 12 a, 12 b may be configured to rotate such that a complementary angle α_(c) between the elongate members 12 a, 12 b, as shown in FIG. 1B, can range from about 0° to 135° in each direction from a coaxial position, and more preferably from about 60° to 135° in each direction from a coaxial position. Once the elongate members 12 a, 12 b are in a desired position relative to one another, which is typically as a result of attaching the terminals ends 13, 15 of the elongate members 12 a, 12 b to an anchoring device, the fastening element 27 can be fully threaded into the bore 28 c in the male connector 20 b to cause the male connector 20 b to engage the mating element 29, thereby preventing rotation of the second elongate member 12 b relative to the first elongate member 12 a.

FIGS. 2A-2B illustrate another embodiment of a spinal fixation device 100 according to the present invention. In this embodiment, the spinal fixation device 100 includes a first elongate member 112 a having a first connecting feature 120 a formed thereon that is matable to a second connecting feature 120 b formed on a second elongate member 112 b. Each connecting feature 120 a, 120 b can have any shape and size, but in the illustrated embodiment the connecting features 120 a, 120 b have a substantially circular shape. Each connecting feature 120 a, 120 b also includes opposed inner and outer surfaces 114 a, 114 b, 116 a, 116 b, and the inner surface 114 a, 116 a of each connecting feature 120 a, 120 b is adapted to be positioned adjacent to one another. As a result, the elongate members 112 a, 112 b are offset from each other such that they are parallel to a plane of rotation. While not shown, one or both elongate members 112 a, 112 b can optionally be angled at any orientation relative to the plane of rotation, such that the elongate member(s) 112 a, 112 b intersects the plane of rotation.

Continuing to refer to FIGS. 2A-2B, the connecting features 120 a, 120 b also each include a central bore 122 a, 122 b extending through the inner and outer surfaces 114 a, 114 b, 116 a, 116 b thereof and adapted to receiving a locking mechanism 127. The locking mechanism 127, when disposed through the central bores 112 a, 112 b, allows the connectors 120 a, 120 b, and consequently the first and second elongate members 112 a, 112 b, to rotate there around. In an exemplary embodiment, each elongate member 112 a, 112 b can rotate 360° relative to one another. One skilled in the art will appreciate that certain applications may require a range of rotation of less than 360°, in which case a restriction, such as a mechanical stop, may be introduced to limit the range of rotation.

The locking mechanism 127 can have a variety of configurations, but in an exemplary embodiment, as shown, the locking mechanism 127 is a threaded member, e.g., a screw, that is similar to threaded member 27 shown in FIGS. 1A-1D. The central bore 122 b in the first elongate member 120 a can be configured to freely, rotatably receive the fastening element 127, and the central bore 122 a in the second elongate member 120 b can be threaded to mate with the threaded shank 127 b of the fastening element 127. In use, when the fastening element 127 is in an unlocked position, it allows the first and second elongate members 112 a, 112 b to freely rotate relative to one another. Once properly positioned, the fastening element 127 can be fully threaded into the central bore 122 b in the second elongate member 120 b, as shown in FIG. 2B, to lock the connectors 120 a, 120 b in a fixed position relative to one another, thereby preventing rotation of the first and second elongate members 112 a, 112 b.

The configuration of the locking mechanism 127 on spinal fixation device 100 is particularly advantageous for use in lumbar or sacral-pelvic fixation. In particular, the fastening element 127 extends through the connecting features 120 a, 120 b in a direction that is substantially perpendicular to the plane of rotation of the elongate members 112 a, 112 b, thus allowing an insertion tool, such as a driver tool, to be used to thread the fastening element 127 into the connecting features 120 a, 120 b when the device 100 is implanted.

In a further embodiment, the inner surface 114 a, 116 a of each connector 120 a, 120 b can optionally include one or more anti-rotation features formed thereon. The anti-rotation features are effective to facilitate locking of the first and second elongate members 112 a, 112 b in a fixed position relative to one another. While various anti-rotation features can be used, each connector 120 a, 120 b can include gear teeth 118 a, 118 b formed thereon for engaging one another when the locking mechanism 127 is fully locked relative to the connectors 120 a, 120 b. In an exemplary embodiment, the gear teeth 118 a, 118 b have a size that allows angular positioning of the first and second elongate members 112 a, 112 b in 4° increments relative to one another, however any increment can be used.

FIGS. 3A-3B illustrate yet another embodiment of a spinal fixation device 100′ in accordance with the present invention. The device 100′ is similar to the device 100 shown in FIGS. 2A-2B, and thus like reference numbers are used to refer to like parts. In this embodiment, the locking mechanism differs in that it includes a pin member 127′, rather than a threaded member 127, that extends through the central bore 122 a, 122 b in each connector 120 a, 120 b. The locking mechanism also includes a fastening element 130 that is adapted to at least partially extend into the pin member 127′ to lock the connectors 120 a, 120 b in a fixed position. The orientation of the fastening element 130′ is particularly advantageous for use in occipital-cervical fixation since the fastening element 130′ extends through the connecting feature 120 b in a direction that is substantially parallel to the plane of rotation of the elongate members 112 a, 112 b.

The pin member 127′ can have a variety of shapes and sizes, but in an exemplary embodiment it has head 127 a′ and a shank 127 b′ having a substantially cylindrical shape to allow the connector members 120 a′, 120 b′ to rotate there around. The head 127 a′ of the pin member 127′ is configured to sit within a recess 132′ formed within an opening of the central bore 122 a′ extending through the first connector 120 a′. The shank 127 b′ of the pin member 127′ is configured to extend through and sit within the bore 122 a′, 122 b′ in each connector 120 a′, 120 b′, and it includes a transverse bore 128′ formed therein for receiving a portion of a fastening element 130′.

The fastening element 130′ preferably includes a proximal threaded shank 131 a′ that is adapted to mate with a threaded receiving bore 132′ formed in the second connector 120 b′, and a distal non-threaded shank 131 b′ that is adapted to extend into the transverse bore 128′ formed in the pin member 127′. In use, the fastening element 130′ can be partially threaded into the threaded bore 132′ formed in the second connector 120 b′ to allow rotation of the first and second elongate members 112 a′, 112 b′ relative to one another. In this position, the non-threaded shank 131 b′ on the fastening element 130′ extends into the transverse bore 128′ in the pin member 127′, and it preferably loosely engages the bore 128′ to allow rotation between the first connector 120 a′ and the second connector 120 b′. Further threading of the fastening element 130′ into the threaded bore 132′ will lock the angular position of the first and second elongate members 112 a′, 112 b′ relative to one another, as shown in FIG. 3B. While various techniques can be used to lock the first and second elongate members 112 a′, 112 b′ relative to one another, in one embodiment the this can be achieved by forming the transverse bore 128′ in the pin member 127′ at a location that is axially offset from the receiving bore 132′ in the second connector 120 b′ when the pin member 127′ is fully disposed therein. Thus, upon further rotation of the fastening element 130′into the receiving bore 132′, the non-threaded shank 131 b′ causes the first connector 120 a′ to translate further toward the second connector 120 b′, thereby locking the connectors 120 a′, 120 b′ in a fixed position relative to one another. In this fixed position, the head of 127 a′ of the pin member 127′ is preferably fully seated within the recess 132′ formed in the bore 122 a′ of the first connector 120 a′. In other embodiments, the transverse bore 128′ and the non-threaded shank 131 b′ can contain features to translation and/or locking of the connectors 120 a′, 120 b′. For example, a portion of the shank 131 b′, e.g., a distal end, and a portion of the transverse bore 128′, e.g., an opening, can include conforming chamfers formed thereon.

As previously described with respect to connector 100 shown in FIGS. 2A-2B, an inner surface of each connector 120 a′, 120 b′ can include anti-rotation features formed therein, such as gear teeth or knurling to prevent rotation of the first and second elongate members 112 a′, 112 b′ relative to one another when the device 100′ is in the locked configuration.

FIGS. 4A-4B illustrate yet another embodiment of a spinal fixation device 400 in accordance with the present invention. In this embodiment, the connecting features 420 a, 420 b on the first and second elongate members 412 a, 412 b each have a substantially elongate, curved configuration such that they include complimentary matable surfaces 470, 472. One of the connecting features, e.g., the first connecting feature 420 a, can include an elongate slot or opening 422 a formed therein, and the other connecting feature, e.g., the second connecting feature 420 b, can include a threaded bore 422 b formed therein. The slot 422 a and bore 422 b are configured to receive a locking mechanism 430 that is effective to lock the first elongate member 420 a in a fixed position relative to the second elongate member 420 b. In an exemplary embodiment, the locking mechanism 430 includes threaded member 432 that can be disposed through the slot 422 a in the first elongate member 420 a, and that is matable with the threaded bore 422 b in the second elongate member 420 b.

In use, when the fastening element 432 is partially threaded into the threaded bore 422 b, the first and second connectors 420 a, 420 b are slidably movable relative to one another, thereby adjusting the angle of the first and second elongate members 412 a, 412 b relative to one another. The radius of curvature can vary depending on the curvature of each connector 420 a, 420 b. Once properly positioned, the fastening element 432 can be fully threaded into the bore 422 b to lock the elongate members 412 a, 412 b in a fixed position and at a fixed angle. A person skilled in the art will appreciate that the locking mechanism can be a rivet, pin, bolt or other fastening device known in the art.

In a further embodiment, the complimentary matable surfaces 470, 472 can include gear teeth formed thereon and adapted to prevent slipping or rotation when the locking mechanism 430 is in a locked position. While a variety of anti-slip features can be formed on the complimentary matable surfaces 470, 472, FIGS. 4A and 4B illustrate gear teeth (only gear teeth 480 on the second connecting feature 420 b are shown) formed thereon.

FIG. 5A illustrates another exemplary embodiment of a spinal fixation device 500 according to the present invention. In general, the connecting feature 520 a, 520 b on each elongate member 512 a, 512 b is in the form of a protrusion that allows polyaxial movement of the elongate members 512 a, 512 b relative to the locking mechanism 530. While the shape of the protrusion 520 a, 520 b can vary, in the illustrated embodiment the each protrusion 520 a, 520 b has a generally bulbous shape. The locking mechanism 530 includes a housing 510 that is adapted to receive the protrusion 520 a, 520 b of each elongate member 512 a, 512 b such that the first and second elongate members 512 a, 512 b are substantially opposed to one another. Additionally, the locking mechanism 530 is adapted to lock the first and second elongate members 512 a, 512 b in a fixed position relative to one another, as shown in FIGS. 5B and 5C.

The housing 510 of the locking mechanism 530 can have a variety of shapes and sizes, but in the illustrate embodiment, the housing 510 has a substantially rectangular shape and it includes a central opening 585 formed therein and extending between opposed top and bottom surfaces 581, 582 thereof. Additionally, the housing 510 has at least two opposed side openings 583 a, 583 b, shown in FIG. 5A, extending from opposed first and second side surfaces 587, 588 thereof. Each elongate member 512 a, 512 b is positioned through the first and second opposed side openings 583 a, 583 b such that the bulbous protrusion 520 a, 520 b formed thereon is seated within the central opening 585 of the housing 510. Preferably, each of the first and second opposed side openings 583 a, 583 b in the housing 510 are sized to have a diameter d₁ that is smaller than a diameter d₂ of the bulbous protrusion 520 a, 520 b on each elongate member 512 a, 512 b to prevent the bulbous protrusions 520 a, 520 b from passing therethrough. The diameter d₁ of the opposed side openings 583 a, 583 b should, however, be larger than the diameter d_(r) of each elongate member 512 a, 512 b to allow the elongate members 512 a, 512 b to extend therethrough and to rotate freely. In an exemplary embodiment, the side openings 583 a, 583 b allow the first and second elongate members 512 a, 512 b to rotate about 60° in all directions relative to the housing 510, and more preferably to rotate in the range of about 30° to 60°. As a result, the first and second elongate members 512 a, 512 b can form an angle in the range of about 0 to 120° relative to one another.

As previously stated, the locking mechanism 530 is also adapted to lock the elongate members 512 a, 512 b in a fixed position relative to one another. While various techniques can be used to lock the elongate members 512 a, 512 b in a fixed position, in the illustrated embodiment the locking mechanism 530 includes a fastening element 590, which can be a screw, rivet, bolt or other fastening device known in the art, that is adapted to mate to a receiver member 592. In the illustrated embodiment, the fastening member 590 is a threaded member having a threaded shank 590 a that is adapted to extend through the central opening 585 to mate with the receiving member 592, and a head 590 b that is adapted to rest against or sit within a portion of the central opening 585 formed in the top surface 581 of the housing.

The receiver member 592 is preferably positioned within a portion of the central opening 585 that is adjacent to the bottom surface 582 of the housing 510, and it has a shape that is effective to lock the bulbous protrusion 520 a, 520 b on each elongate member 512 a, 512 b in a fixed position within the central opening 585 when the fastening element 590 is mated thereto. In particular, the receiving member 592 can have a substantially rectangular shape, as shown in FIG. 5C, and it can include opposed concave side surfaces 592 a, 592 b formed thereon. In use, the fastening element 590 can be threaded into a corresponding threaded bore 592 c extending through the receiving element 592 to engage the receiving element 592 and pull it into the central bore 585 formed in the housing 510. As the receiving element 592 moves into the central bore 585, the opposed side surfaces 592 a, 592 b abut against the bulbous protrusion 520 a, 520 b on each elongate member 512 a, 512 b to lock the protrusions 520 a, 520 b in a fixed position relative to the housing 510.

A person skilled in the art will appreciate that the configuration of the protrusion 520 a, 520 b on each elongate member 512 a, 512 b and the receiving element 592 can vary. For example, each connecting features 520 a, 520 b can have a substantially concave recess formed therein, and the receiving element 592 can include convex side surfaces formed thereon for engaging the connecting features 520 a, 520 b.

It is possible that some applications will require angular adjustability of only one of the elongate members. Accordingly, in each of the various embodiments of the present invention, one of the elongate members can be angularly adjustable and the other elongate member can maintained in a fixed position.

One skilled in the art will appreciate further features and advantages of the invention based on the above-described embodiments. Accordingly, the invention is not to be limited by what has been particularly shown and described, except as indicated by the appended claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety. 

What is claimed is:
 1. A spinal fixation assembly comprising: a first member having a first base and a first rod extending outward from the first base; an extension shaft extending outward from the first base, the extension shaft having a first end and a second end, the second end being spaced away from the first base; a second member having a second base and a second rod extending outward from the second base, the second member having a receiving section formed in the second base in which the second end of the extension shaft is received; and a fastener extending through the second base and into the receiving section, the fastener having a contact surface that contacts the extension shaft to lock the second base to the first base and prevent the first member from rotating relative to the second member.
 2. The assembly of claim 1, wherein the fastener extends through an opening in the second base and into the receiving section along a first axis that is substantially perpendicular to a second axis formed by the extension shaft.
 3. The assembly of claim 1, wherein the first rod and the extension shaft are substantially perpendicular.
 4. The assembly of claim 1, wherein the fastener contacts the second end of the extension shaft.
 5. A spinal fixation assembly comprising: a first member having a first base and a first rod extending outward therefrom; a second member having a second base and a second rod extending outward therefrom; an extension shaft extending outward from the first base and into an interior section formed by a wall of the second base; and a fastener to lock the second base to the first base to prevent rotation of the first member relative to the second member, the fastener being spaced away from the first and second rods and extending from the second base and into contact with the extension shaft; wherein the fastener extends through the wall of the second base and into the interior section along an axis that is substantially perpendicular to a longitudinal axis of the extension shaft.
 6. The assembly of claim 5, wherein the first rod is integrally formed with the first base, and the second rod is formed integrally with the second base.
 7. The assembly of claim 5, further comprising a plurality of interlocking features formed on each of the first and second bases that engage together when the fastener locks the second base to the first base. 